diff -urpa postgresql-13.1.orig/src/bin/pg_upgrade/option.c postgresql-13.1/src/bin/pg_upgrade/option.c
--- postgresql-13.1.orig/src/bin/pg_upgrade/option.c	2020-11-09 23:24:30.000000000 +0100
+++ postgresql-13.1/src/bin/pg_upgrade/option.c	2020-12-03 20:58:30.431778786 +0100
@@ -476,8 +476,14 @@ get_sock_dir(ClusterInfo *cluster, bool
 	 */
 	if (GET_MAJOR_VERSION(cluster->major_version) >= 901)
 	{
-		if (!live_check)
+		if (!live_check) {
 			cluster->sockdir = user_opts.socketdir;
+#ifndef UNIX_PATH_MAX
+#define UNIX_PATH_MAX 108
+#endif
+			if (strlen(cluster->sockdir) >= UNIX_PATH_MAX - sizeof(".s.PGSQL.50432"))
+				strcpy(cluster->sockdir, "/tmp"); /* fall back to tmp */
+		}
 		else
 		{
 			/*
diff -urpa postgresql-13.1.orig/src/include/pg_config_manual.h postgresql-13.1/src/include/pg_config_manual.h
--- postgresql-13.1.orig/src/include/pg_config_manual.h	2020-11-09 23:24:30.000000000 +0100
+++ postgresql-13.1/src/include/pg_config_manual.h	2020-12-03 20:59:32.262778786 +0100
@@ -201,7 +201,7 @@
  * support them yet.
  */
 #ifndef WIN32
-#define DEFAULT_PGSOCKET_DIR  "/tmp"
+#define DEFAULT_PGSOCKET_DIR  "/var/run/postgresql"
 #else
 #define DEFAULT_PGSOCKET_DIR ""
 #endif